16 STUDIES IN GENERAL PHYSIOLOGY 
the latter are concerned, it is wrong, as we shall see, to say 
that certain animals ‘‘are fond of the light” and seek those 
regions in space where light is most intense, while others “are 
fond of the dark” and betake themselves to those regions 
which are darkest. In contradiction of this idea I shall 
prove that the direction of the progressive heliotropic move- 
ments of animals is determined solely by the direction of the 
rays, no matter whether the animals move from regions in 
which light is less intense to those in which it is more 
intense, or vice versa. 
Further than this, it is fundamentally wrong to say that 
an assumed ‘‘preference for color” determines the orientation 
of animals toward rays of different refrangibilities; that, 
as Graber says, the animals which “are fond of blue” “hate 
red,” and that those which “are fond of red” ‘‘hate blue.” 
In contradiction of this idea I shall prove that there are no 
animals which “are fond of” red or “hate” blue, but only 
such as move toward a source of light or away from it; and 
that these movements occur in the same way under the 
influence of the more refrangible rays as under that of the 
less refrangible rays, only with this purely quantitative 
difference, that the more refrangible rays, as in plants, are 
much more effective than the less refrangible ones, which 
usually have no effect. 
I consider it inadvisable to represent the movements ob- 
served in animals as the expression of a “color preference,” 
or a “color sensation,” of a “pleasurable” or ‘“unpleasur- 
able sensation,” as do most animal physiologists and zoélo- 
gists who have studied the effects of light in the animal 
kingdom. I do not propose to base an analysis of the 
movements of animals on such hypothetical, anthropomorphic 
sensations and feelings, but on such conditions as determine 
the course of phenomena in inanimate nature as well. Real 
natural science began when, instead of fabulizing over the 
Digitized by Microsoft® 
